Global Structure of Low-Latitude and Equatorial Geomagnetic Pulsations Associated with Storm Sudden Commencements.

Itonaga, M.; Matsuzono, Kosuke; Kitamura, Teitaro; Toshimitsu, I.; Trivedi, N. B.; Horita, R. E.; Watanabe, T.; Riddick, John C.

doi:10.5636/jgg.47.441

Cited by 8 publications

(3 citation statements)

References 14 publications

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“…Yumoto et al, 1992Yumoto et al, , 1996Itonaga et al, 1995). Quantitative analysis on the basis of data analysis along with the computer simulation is now and will be further developed in the S-RAMP period to clarify more precisely the processes in the magnetosphere and the ionosphere.…”

Section: Introductionmentioning

confidence: 99%

Characteristics of geomagnetic sudden commencement observed in middle and low latitudes

Tsunomura¹

2014

Earth Planet Sp

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Characteristics of geomagnetic sudden commencement (SC) observed in middle and low latitudes are discussed on the basis of data analyses of magnetic variations and a numerical calculation. From the data analyses, it is found that a negative impulse is usually superposed on the main impulse of SC in H component just after its onset, at the stations in middle to high latitudes in the local time range from the morning to the early afternoon. The superposition of the negative impulse causes the decrease of SC amplitude in H component with increasing latitude in this area. The occurrence of the negative impulse does not seem to be dependent on geomagnetic activity. Examining a case study and a numerical analysis, it is suggested that this negative impulse is a signature of the magnetic variation due to the polar-originated ionospheric current system responsible for the main impulse of SC (DP MI ). The discussion includes the possible interpretation of PPI introduced by Kikuchi and Araki (1985) and the availability of D component magnetic data in middle latitude for a rough estimation of the magnetosphere-ionosphere coupling process.

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Section: Introductionmentioning

confidence: 99%

Characteristics of geomagnetic sudden commencement observed in middle and low latitudes

Tsunomura¹

2014

Earth Planet Sp

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“…If the global modulation prevails commonly in the inner magnetosphere, low-latitude and equatorial geomagnetic pulsations, which are considered to originate in compressional waves, must have continuous spectral structures. That is not the case and they actually show discrete spectral structures (Itonaga et al, 1992(Itonaga et al, , 1995. Then, although there may exist certainly the local modulation of compressional wave by the eigenoscillation of field line around the magnetic equator, it appears that the modulation can be globally neglected.…”

Section: Discussionmentioning

confidence: 94%

The Excitation of Shear Alfven Wave and the Associated Modulation of Compressional Wave in the Inner Magnetosphere.

Itonaga

Yoshikawa

1996

J. geomagn. geoelec

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Two basic but novel equations directly describing the generation of shear Alfven and compressional waves in the inner magnetosphere filled with a cold magnetized plasma are derived. The shear Alfven wave is characterized by the field-aligned current and the compressional wave by the compressional component of the magnetic field. Such a generation arises from the effects of inhomogeneous Alfven speed and curvilinear field line. Around the magnetic equator, if the Alfven speed is inversely proportional to a power of the geocentric distance, these effects have magnitudes of the same order and their signs are identical.Considered in the present study is a situation that the earthward propagating compressional wave is launched from a large scale oscillating current wedge centered at midnight and symmetric about the magnetic equator. Then, it is found that the field-aligned current excited around the equator by the compressional wave has opposite senses in direction in the northern and southern hemispheres, in the pre-and post-midnight sectors as well as just inside the plasmapause and in its surrounding regions. As a result of the excitation of shear Alfven wave, two types of oscillations appear on a field line: One is a forced oscillation and the other is an eigenoscillation. Although a modulation of the compressional wave may be caused locally (or microscopically) around the equator by the eigenoscillation of field line, the modulation can be globally (or macroscopically) neglected. So far as the propagation along the source longitude (source-earth line) around the equator is concerned, the coupling between compressional and shear Alfven waves can be almost neglected and so one-dimensional response of the inner magnetosphere around the equator plays a significant role in the compressional oscillation.

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“…In order to examine it strictly, wave equations in the ionosphere-atmosphere-Earth region should be used and be solved. However the wave equations are not simple [e.g., Itonaga et al, 1997], therefore we present the coupling by using the simplified model in this paper. It may be simplified too much, but, it is a valuable analysis of the equatorial phase lag as the initial discussion.…”

Section: Summary and Discussionmentioning

confidence: 99%

Wave characteristics of geomagnetic pulsations across the dip equator

et al. 1998

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Abstract. In order to clarify the wave characteristics of Pi2 and Pc 4-5 magnetic pulsations around the dip equator, we analyzed magnetic data from the latitudinally dense magnetometer array in Brazil. We found that the phase difference between Pi2 pulsations observed at globally separated low-latitude stations is small, whereas Pi2 pulsations observed within the dayside dip equator region of 5:2 ø latitude show phase lags of about 30 ø • 50 ø behind those in the off-dip equator region. Pc 4-5 magnetic pulsations at the dip equator also show the same phase character. Pi2 amplitudes are enhanced in the equatorial region, where the phase lags of pulsations must be associated with the enhancement of ionospheric conductivity. The equatorial phase lags can be explained by invoking the induction effect of the equatorial enhanced ionospheric current above the good conductor Earth.

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Global Structure of Low-Latitude and Equatorial Geomagnetic Pulsations Associated with Storm Sudden Commencements.

Cited by 8 publications

References 14 publications

Characteristics of geomagnetic sudden commencement observed in middle and low latitudes

Characteristics of geomagnetic sudden commencement observed in middle and low latitudes

The Excitation of Shear Alfven Wave and the Associated Modulation of Compressional Wave in the Inner Magnetosphere.

Wave characteristics of geomagnetic pulsations across the dip equator

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